Information Technology Reference
In-Depth Information
CHAPTER THIRTEEN
OPTIMIZATION
Aspen Plus's focus in the area of process optimization is limited primarily to appli-
cations involving process models constructed using Aspen Plus. As examples, process
optimization can refer to selection of the optimal operating conditions of process equip-
ment, or optimal design of equipment, each subject to the definition of “optimal.” These
conditions, or design variables, could be driven by “lowest cost,” or “easiest to con-
trol,” or any other basis of evaluation. The applications are typically characterized by a
function that is to be maximized or minimized subject to variables that are meaningful
within limits; for example, a negative mole fraction has no meaning within a process. In
the classical sense, such problems are formally described by an objective function and
constraints on the independent variables. A formal example of an objective function
is given by
=
(x
1
,x
2
,...,x
n
)
(13.1)
where
x
1
,x
2
,...,x
n
refer to the independent variables. An example of an equality
constraint,
f
1
,isgivenby
f
1
=
f
1
(x
1
,x
2
,...,x
n
)
=
0
(13.2)
and an inequality constraint,
f
2
,
by
f
2
=
f
2
(x
1
,x
2
,...,x
n
)
≤
0
(13.3)
The variables that define the constraints and the objective function need not necessarily
be continuous but may take on only integer values. The objective function has one
value for a given set of independent variables. The problem is to find the set of
